A Ranking cycle system is described in Japanese Patent Application Laid-open No. 58-48706, which is designed, so that a high-pressure gas-phase operating medium generated by heating a liquid-phase operating medium in an evaporator is expanded in an expander to take out a mechanical energy, and the resulting low-pressure gas-phase operating medium is cooled in a condenser and restored to a liquid-phase operating medium, which is supplied again to the evaporator by a pump. In the above-described conventional system, an expander of a vane-type is used as a rotary fluid machine constituting the expander.
It should be noted here that in the expander of the vane-type, it is necessary to lubricate a bearing portion of the output shaft rotated in unison with a rotor and sliding portions of vanes radially movably supported on the rotor. However, the sliding portions are exposed to severe conditions of a high temperature and a high pressure and hence, there is a possibility that the seizure and the wearing may occur, if an effective lubricating means is not employed.
In the expander of the vane-type, vanes reciprocally movably supported in slot-shaped spaces provided radially in the rotor are pushed circumferentially by the gas-phase operating medium supplied to a rotor chamber to rotate the rotor. For this reason, a special lubricating means is required in order to prevent the occurrence of the seizure and wearing due to the gouging generated in the sliding portion of vane in the slot-shaped space.
Further, the expander of the vane-type suffers from the following problem: It is necessary to provide a clearance as large as 50 μm on one side between side faces of the rotor and an inner surface of the casing in order to permit the deflection generated due to a clearance at the bearing portion of the rotor, and the high-pressure gas-phase operating medium in the rotor chamber may be leaked from the clearance. If a common contact-type seal member is used in order to prevent the leakage of the gas-phase operating medium from the clearance between the side face of the rotor and the inner surface of the casing, not only a loss due to the friction is produced, but also the durability of the seal member is feared. In addition, it is substantially difficult to achieve the sealing with the clearance between the side face of the rotor and the inner surface of the casing being simply decreased, because of the limit of the accuracy of the bearing portion of the rotor.
If an annular seal means is disposed between each of the side faces of the rotor and the inner surface of the casing in order to prevent the leakage of the gas-phase operating medium from the clearance between the side face of the rotor and the inner surface of the casing, then the pressure of the gas-phase operating medium in the rotor chamber is not constant in a circumferential direction, and is high in an expansion stroke of the gas-phase operating medium and low in an exhaust stroke of the gas-phase operating medium. Therefore, if a sealing force required in the expansion stroke in which the pressure is high is provided equally over the entire periphery of the annular seal means, the following problem is encountered: The sealing force is excessive in the exhaust stroke in which the pressure is low and hence, the useless frictional resistance is increased, resulting in an energy loss.